docs: def validate_ceph_pool_samples(self, samples, sample_type="resource pool"):
          """Validate ceph pool samples taken over time, such as pool
          object counts or pool kb used, before adding, after adding, and
          after deleting items which affect those pool attributes.  The
          2nd element is expected to be greater than the 1st; 3rd is expected
          to be less than the 2nd.
  
          :param samples: List containing 3 data samples
          :param sample_type: String for logging and usage context
          :returns: None if successful, Failure message otherwise
          """
          original, created, deleted = range(3)
          if samples[created] <= samples[original] or \
                  samples[deleted] >= samples[created]:
              return ('Ceph {} samples ({}) '
                      'unexpected.'.format(sample_type, samples))
          else:
              self.log.debug('Ceph {} samples (OK): '
                             '{}'.format(sample_type, samples))
              return None